In a vehicle crash, the knee of a vehicle occupant is frequently susceptible to injury. A significant number of knee injuries results from impact forces on the leg that cause the lower leg (tibia) to travel in an opposite direction to the path of the upper leg (femur). As a consequence of this motion, the tibia shears relative to the femur, causing ligaments and tendons in the knee to tear.
Existing knee bolsters fail to address this shearing effect. For example, one such design merely deploys an air bag in the vicinity of the knee of the occupant. However, such an air bag does not prevent movement of the knee relative to the tibia because the air bag contacts both the knee and the tibia in deployment.
An alternative knee bolster design uses a mechanical carriage to direct a padded cushion toward the knee of the vehicle occupant. This design advances the padded cushion through a telescoping support. The telescoping support expands through either a spring or a pyrotechnic force within the telescoping support. This alternative design does not offer the benefits of cushioning a vehicle impact with an air bag.
A need therefore exists for a knee bolster that uses an air bag to stop movement of the femur relative to the tibia.